Numerical investigation on vibration isolation by softer in-filled trench barriers

2016 ◽  
Vol 3 (1) ◽  
pp. 31-42 ◽  
Author(s):  
Ankurjyoti Saikia
Keyword(s):  
Shear Wave ◽  
Half Space ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Vibration Isolation ◽  
Engineering Practice ◽  
Homogeneous Half Space ◽  
Surface Displacements ◽  
Surface Vibrations ◽  
Infill Material

This paper deals with a 2-D finite element study in PLAXIS 2D on isolation of steady-state surface vibrations by softer backfilled trenches in an elastic, isotropic, and homogeneous half-space. Effects of barrier geometric features and infill material characteristics on reducing vertical and horizontal components of surface displacements are investigated. This study adopts a non-dimensional approach where the geometric parameters are normalized against the Rayleigh wavelength of vibration in half-space and backfill shear wave velocity is expressed as a ratio of that of parent soil. Softer barriers of shear wave velocity ratios less than unity are considered as they are found significantly effective than stiffer barriers. Effects of the parameters participating on wave isolation are extensively discussed and some guidelines are framed regarding their optimal selection. Non-dimensional charts are developed which would provide a sound basis for designing such barriers in actual engineering practice. The design charts are validated with some documented results and close agreement is obtained.

Estimation Study on Shear Wave Velocity of Seabed Using GRNN

2014 ◽  
Vol 580-583 ◽  
pp. 264-267
Author(s):  
Sheng Jie Di ◽  
Zhi Gang Shan ◽  
Xue Yong Xu
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Seismic Analysis ◽  
Site Response ◽  
Estimation Method ◽  
Response Analysis ◽  
Generalized Regression Neural Network ◽  
Engineering Practice ◽  
Site Classification

Characterization of the shear wave velocity of soils is an integral component of various seismic analysis, including site classification, hazard analysis, site response analysis, and soil-structure interaction. Shear wave velocity at offshore sites of the coastal regions can be measured by the suspension logging method according to the economic applicability. The study presents some methods for estimating the shear wave velocity profiles in the absence of site-specific shear wave velocity data. By applying generalized regression neural network (GRNN) for the estimation of in-situ shear wave velocity, it shows good performances. Therefore, this estimation method is worthy of being recommended in the later engineering practice.

Shear horizontal surface acoustic waves in a magneto-electro-elastic system

2016 ◽  
Vol 25 (1-2) ◽  
pp. 1-13 ◽  
Author(s):  
Shahin Eskandari ◽  
Hossein M. Shodja
Keyword(s):  
Power Series ◽  
Shear Wave ◽  
Half Space ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Acoustic Waves ◽  
Series Solution ◽  
Surface Acoustic Waves ◽  
Power Series Solution ◽  
Shear Horizontal

AbstractPropagation of shear horizontal surface acoustic waves (SHSAWs) within a functionally graded magneto-electro-elastic (FGMEE) half-space was previously presented (Shodja HM, Eskandari S, Eskandari M. J. Eng. Math. 2015, 1–18) In contrast, the current paper considers propagation of SHSAWs in a medium consisting of an FGMEE layer perfectly bonded to a homogeneous MEE substrate. When the FGMEE layer is described by some special inhomogeneity functions – all the MEE properties have the same variation in depth which may or may not be identical to that of the density – we obtain the exact closed-form solution for the MEE fields. Additionally, certain special inhomogeneity functions with monotonically decreasing bulk shear wave velocity in depth are considered, and the associated boundary value problem is solved using power series solution. This problem in the limit as the layer thickness goes to infinity collapses to an FGMEE half-space with decreasing bulk shear wave velocity in depth. It is shown that in such a medium SHSAW does not propagate. Using power series solution we can afford to consider some FGMEE layers of practical importance, where the composition of the MEE obeys a prescribed volume fraction variation. The dispersive behavior of SHSAWs in the presence of such layers is also examined.

Effects of Local Site Conditions on Seismic Responses of a Reactor Containment Structure

2006 ◽  
Author(s):  
Jian-Chu Chen
Keyword(s):  
Shear Wave ◽  
Half Space ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Response Spectra ◽  
Site Conditions ◽  
Pressurized Water ◽  
Soil Thickness ◽  
Local Site ◽  
Local Site Conditions

The effect of local site conditions on soil-structure interaction (SSI) responses of a pressurized water reactor (PWR) containment building founded on different site conditions was investigated using substructure SSI analysis procedure. The structure was analyzed for both surface and embedded foundation conditions for each site with an exception for one half-space site with shear wave velocity 5000 fps. Only the surface foundation was analyzed for this very stiff half-space site. A total of 23 analyses are presented in this paper. Responses including peak ground accelerations and response spectra at selected locations were compared. The results indicate that the local site conditions have a significant influence on SSI response particularly for the structure founded on the surface of shallow soil deposit overlying competent rock. For thick soil sites having shear wave velocity larger than 1000 fps and having soil thickness greater than 3.5 times the radius of the structure, the effect of the soil thickness is not important.

scholarly journals Dispersion of Love Waves in a Composite Layer Resting on Monoclinic Half-Space

2011 ◽  
Vol 2011 ◽  
pp. 1-9
Author(s):  
Sukumar Saha
Keyword(s):  
Shear Wave ◽  
Half Space ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Velocity Ratio ◽  
Composite Layer ◽  
Love Waves ◽  
Isotropic Layer ◽  
Ratio Curve ◽  
Wave Velocity Equation

Dispersion of Love waves is studied in a fibre-reinforced layer resting on monoclinic half-space. The wave velocity equation has been obtained for a fiber-reinforced layer resting on monoclinic half space. Shear wave velocity ratio curve for Love waves has been shown graphically for fibre reinforced material layer resting on various monoclinic half-spaces. In a similar way, shear wave velocity ratio curve for Love waves has been plotted for an isotropic layer resting on various monoclinic half-spaces. From these curves, it has been observed that the curves are of similar type for a fibre reinforced layer resting on monoclinic half-spaces, and the shear wave velocity ratio ranges from 1.14 to 7.19, whereas for the case isotropic layer, this range varies from 1.0 to 2.19.

Radiation patterns of torsionally vibrating seismic sources

Geophysics ◽  
1984 ◽  
Vol 49 (8) ◽  
pp. 1213-1222 ◽  
Author(s):  
Geoffrey A. Dorn
Keyword(s):  
Surface Layer ◽  
Radiation Pattern ◽  
Shear Wave ◽  
Half Space ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Layered Medium ◽  
Radial Distance ◽  
Far Field ◽  
Radiation Patterns

The radiation patterns available in the literature for seismic surface sources are restricted to far‐field, low‐frequency solutions for undamped half‐space models. A theoretical study of the radiation pattern of a circular baseplate vibrating torsionally on the surface of an N-layered anelastic medium demonstrates that the patterns in the literature do not reasonably represent the radiated field of a source on a damped layered medium. The radiation pattern of a source is a measure of the strength of the output signal as a function of direction and is determined by calculating the displacements at points along the arc of a circle at a specified radial distance from the source. The solution for the displacement due to a vibrator or a plane‐layered anelastic medium is obtained by solving the elastodynamic wave equation using Fourier and Hankel transforms. The displacement is expressed in terms of an inverse Hankel transform which is performed numerically. The shape of the torsional radiation pattern in a half‐space is a function of frequency, baseplate radius, shear‐wave velocity, and radial distance between the source and the observation points. As frequency increases, the source beams more energy in a near‐vertical direction, and less in directions near the horizontal. Vertical beaming also increases as baseplate radius increases and as shear‐wave velocity decreases. The radiated field approaches an asymptotic far‐field radiation pattern at radial distances in excess of 5 to 8 baseplate radii. In a layered medium, constructive and destructive interference of direct, reflected, and refracted waves results in a characteristic lobate structure in the radiated field. A minimum occurs just below the layer interface due to the combined effects of reflections and refractions. As frequency increases, a greater proportion of energy penetrates the layer interface and enters the underlying medium. At frequencies typically used in exploration seismology the majority of the signal from a torsional source is trapped in the surface layer. The shape of the radiation pattern at a given distance from the source is a function of the density, velocity, and Q contrasts between layers. For a given acoustic impedance contrast, more energy is trapped in the surface layer if the contrast is caused primarily by a velocity rather than a density change since the velocity contrast results not only in reflections but also in refractions and Love waves. A variation in Q between layers further distorts the radiated field. The pattern for a layered model does not asymptote to a far‐field pattern until the radial distance is much greater than the total thickness of the layers in the model. Radiation pattern modeling for layered media may help resolve the discrepancies between theoretical patterns and field measurements and may provide a means of optimizing the radiated field of a surface source or source array in terms of its directivity and the partitioning of energy between various wave types.

scholarly journals Selection of an Appropriate Bedrock for Site Amplification Studies.

2021 ◽  
Author(s):  
Bhavesh Pandey ◽  
Ravi S Jakka
Keyword(s):  
Shear Wave ◽  
Half Space ◽  
Fundamental Frequency ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Reference Site ◽  
Strong Motion ◽  
Site Amplification ◽  
A Site ◽  
Selection Of

Abstract The selection of half-space or reference sites significantly influences site amplification studies. However, there are no well-defined guidelines in the literature. Generally, a layer with a local shear wave velocity (VS) of more than 760 m/s is considered a bedrock/half-space/reference site. This study attempts to formulate a rationale for selecting bedrock stiffness to be used as a half-space/reference site. For this study, VS,30 (average shear wave velocity of top 30-meter soil strata from shear wave velocity measurements) and the site's fundamental frequency (obtained from Horizontal to vertical spectral ratio of ambient vibration records) were used as proxies to study the influence of bedrock/half-space and development of a rationale for their selection. This study uses strong-motion data from India's sixty-two strong motion stations and a few from Japan (Kik-Net). The results suggest that considering a site with a shear wave velocity of 760 m/s may not be suitable as a half-space/bedrock for most geomorphological conditions. The results also recognize a pattern that can help in the development of a mathematical model for determining the bedrock for a site using VS,30 and its fundamental frequency as a proxy.

scholarly journals Calibrating a new attenuation curve for the Dead Sea region using surface wave dispersion surveys in sites damaged by the 1927 Jericho earthquake

Solid Earth ◽  
2019 ◽  
Vol 10 (2) ◽  
pp. 379-390 ◽  
Author(s):  
Yaniv Darvasi ◽  
Amotz Agnon
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Dead Sea ◽  
Attenuation Curve ◽  
Surface Wave Dispersion ◽  
Near Surface ◽  
Moderate Seismicity ◽  
Local Point ◽  
The Dead

Abstract. Instrumental strong motion data are not common around the Dead Sea region. Therefore, calibrating a new attenuation equation is a considerable challenge. However, the Holy Land has a remarkable historical archive, attesting to numerous regional and local earthquakes. Combining the historical record with new seismic measurements will improve the regional equation. On 11 July 1927, a rupture, in the crust in proximity to the northern Dead Sea, generated a moderate 6.2 ML earthquake. Up to 500 people were killed, and extensive destruction was recorded, even as far as 150 km from the focus. We consider local near-surface properties, in particular, the shear-wave velocity, as an amplification factor. Where the shear-wave velocity is low, the seismic intensity far from the focus would likely be greater than expected from a standard attenuation curve. In this work, we used the multichannel analysis of surface waves (MASW) method to estimate seismic wave velocity at anomalous sites in Israel in order to calibrate a new attenuation equation for the Dead Sea region. Our new attenuation equation contains a term which quantifies only lithological effects, while factors such as building quality, foundation depth, topography, earthquake directivity, type of fault, etc. remain out of our scope. Nonetheless, about 60 % of the measured anomalous sites fit expectations; therefore, this new ground-motion prediction equation (GMPE) is statistically better than the old ones. From our local point of view, this is the first time that integration of the 1927 historical data and modern shear-wave velocity profile measurements improved the attenuation equation (sometimes referred to as the attenuation relation) for the Dead Sea region. In the wider context, regions of low-to-moderate seismicity should use macroseismic earthquake data, together with modern measurements, in order to better estimate the peak ground acceleration or the seismic intensities to be caused by future earthquakes. This integration will conceivably lead to a better mitigation of damage from future earthquakes and should improve maps of seismic hazard.

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